Search smh:

Search in:

Scientist untangled the wiring of memory

SIR GABRIEL HORN, 1927-2012 Professor Sir Gabriel Horn was a neurobiologist who elucidated the neural mechanisms of learning and memory; from 1992 to 1999 he was Master of Sidney Sussex College, Cambridge.Horn’s first scientific publication, while a medical student at the University of Birmingham, was entitled The Neurological Basis of Thought, which anticipated much of his subsequent work. At an early stage in his career he became interested in the ways in which modification of synaptic transmission (synapses are structures in the nervous system that allow cells known as neurons to pass electrical or chemical signals to other cells) might be responsible for memory. For materialist theories of the mind, it is axiomatic that memory – both the process of learning and the process of recall or re-expression – must in some way be explicable in terms of a change in brain structure. But scientists have continually been frustrated by the difficulty of locating any specific memory “site”.In the 1960s Horn focused on the phenomenon of habituation, a form of learning characterised by a progressive reduction in the behavioural response to a repetitive stimulus. Using microelectrodes in the brains of anaesthetised rabbits, he found neurons in part of the brain called the optic tectum that (as expected) responded strongly to visual stimulus, but whose response declined the more frequently the stimulus was applied, showing habituation. “I suddenly realised that we were dealing with a neural counterpart to behavioural habituation,” he recalled. During subsequent research on the relatively simple giant synapse of the squid, Horn produced evidence that the “waning” response was due to local changes in the synapse rather than to changes in an extended neural network.Horn was a Fellow of King’s College, Cambridge, where, one evening in the mid-1960s, he found himself at High Table sitting next to Patrick Bateson, who had been working on “behavioural imprinting” — the process by which young animals such as domestic chicks rapidly form a social preference from a conspicuous visual stimulus, such as the presence of the Mother Hen. As Horn and Bateson talked, they realised that imprinting would be an excellent form of learning through which to study the neural basis of memory since an animal undergoing “imprinting” has virtually no prior visual experience. They agreed to collaborate, and the biochemist Steven Rose was subsequently drawn into the collaboration.They soon identified biochemical changes in the chicks’ brains, but in order to be sure that these changes were the consequence of imprinting, they devised a series of ingenious experiments to rule out alternative explanations for the changes. One procedure involved comparing two groups of chicks, one of which had had extensive experience with the imprinting object and the other of which had had limited experience. The chicks that had more to learn showed greater biochemical activity.Subsequently, with other collaborators, Horn and Bateson used this technique to identify the area of the brain involved — now known as the intermediate medial mesopallium or IMM. When the IMM was excised before imprinting or immediately afterwards, the chick behaved as if it had no recall, though in other ways it behaved normally, showing that the IMM serves as a storage site for the memory underlying imprinting.Gabriel Horn was born in Birmingham on December 9, 1927. His grandparents were Jewish immigrants from Eastern Europe. He attended Handsworth Technical School having failed the 11-plus, and left school aged 16 to work in his father’s tailoring business. He studied part time for a National Certificate in Mechanical Engineering, achieving a distinction. Then, after National Service in the RAF, he studied Medicine at the University of Birmingham, where he became chairman of the debating and political societies and began to develop an interest in the brain out of a fascination with philosophical issues surrounding consciousness.Horn’s first paper on the neurological basis of thought so impressed the Professor of Anatomy, Solly Zuckerman, that he sent a copy to the philosopher AJ Ayer, who invited Horn to visit him at his Mayfair flat. But as Horn recalled later, the encounter was not a productive one: “He harangued me on how wrong I was and [insisted] that physiology had nothing to say about sensory perception. I occasionally drew his attention to what Bertrand Russell had said which only inflamed him all the more.”In 1956 Horn was Demonstrator in Anatomy and subsequently University Lecturer and then Reader in Neurobiology at Cambridge University. From 1974 he was Professor of Anatomy at the University of Bristol. Appointed to the Cambridge Chair of Zoology in 1977, he served as Head of Department from 1978 to 1994.Under Horn’s leadership, the Department of Zoology developed a wide range of approaches, from the molecular to the ecological, and the number of students reading Part II Zoology more than doubled. In 1992 he was elected Master of Sidney Sussex College, beating Germaine Greer (“They closed ranks,” she was quoted as saying. “I’m relieved – who would want to be Mistress of the dullest college in Cambridge?”). He served as Deputy Vice-Chancellor of the university from 1994 to 1997 and in 1998 he initiated and became chairman of the Cambridge University Government Policy Programme, set up to provide scientific policy advice to the government.After his retirement from the Mastership of Sidney Sussex in 1999, Horn chaired a government committee to review the causes and origins of BSE, concluding in 2001 that the cattle disease was almost certainly the result of young calves being fed material contaminated with sheep scrapie — the result of a change in rendering methods in the 1970s. Subsequently he chaired the Academy of Medical Sciences committee on Brain Science Addiction and Drugs which published an influential report in 2008.He was elected a Fellow of the Royal Society in 1986 and awarded the Society’s Royal Medal in 2001. In 2002 he was knighted for services to neurobiology. He remained a fellow of King’s College, Cambridge, until his death.Gabriel Horn married first, in 1952, Anne Soper, the daughter of the Reverend Donald Soper, with whom he had two sons and two daughters. The marriage was dissolved and in 1980 he married, secondly, the wildlife artist Priscilla Barrett. She and his four children survive him.Telegraph, London

Most Commented

Special offers

Hodson's daughter: Witness protection not safe

"I feel sorry for anyone coming into witness protection," says the tearful daughter of police informer Terence Hodson after the State Coroner delivered an open finding into his murder and that of his wife Christine in 2004.